Chemical composition and process for soil stabilization



1 O 6 7 4e Ep/ t v 7' Whurgen United States Patent- O ce ,j'fiifiilf wherein R is selected from the group consisting of hydro- 2968'572 gen, lower alkyl groups such as methyl, ethyl, propyl, CHEMICAL COMPOSITION AND PROCESS FOR butyl, isomers thereof or the like, -coNH,, lower alkyl- SIZABHIZATLON CONH, groups, wherein the lower alkyl portion meth- Cletns Peelltitl'bil'e, Pamesl ewgnd io t yl, ethyl, propyl, butyl, isomers thereof, or the like, and mofmnelawan mp3?! water-soluble salts of the foregoing, e.g., alkaline earth metal salts (Ca, Ba and/or Sr) or alkali metal salts and No Drawing. Filed July 21, 1958, Ser. No. 749,631 acetates specific illustrative amides are 6 Chum- (M.P. 2.5 c. which is 1o amide, bu rnide or the'flili'e. In some gg igfigg 23:; to 95: 2: 3 x;? m aria: e si ion of this invention addi honally contains an g PO51 additive for imparting an initial high degree of water fi fim 32 11 g; invention relates to insolubility. Such an additive is described hereinafter in some detail.

i Improved method of strengthening by 1 As used in the specification and claims, the term alkali c a? i h 1 th f metal silicate is intended to refer to alkali metal silicates as g z gggi ai g s g gz g g gs zzg g z having an alkali metal oxidezsilicon dioxide molar ratio within therange from about l.0:3.04 notably sodium to be strengthened and/or rendered fluid impermeable is welhknown at this e In some instances the Prior silicate having an N3 O.Sl 2 ratio within the range of about 1:3.0-4.0, the preferred Na O:S iO, ratio being :2: 35: :1 g gs fg g r e f ig fgz i gagg lNa,O to about 3-3.5 810,, and the specifically preferred g y e 9 material being an aqueous sodium silicate having an and soil-treating compositions have been subject to one D or more problems which heretofore have limited the apg g f' igz 2:2, fi ig i zyp g ffi of cltliemlcal g i ed th tion and claims is intended to refer to the various alkali prac Ce gener y as v c succes e metals, i.e., sodium, potassium, lithium, rubidium, cesium i P feparatehhqmdsafne si z gzi and mixtures thereof. Silicates of potassium and sodium me a sue as a 5 mm e s are more generally available. Because of their lower the other a gelling liquid such as calcium chloride re- 3. cost and availability, sodium sihcatcs are more widely as: arizast s ssissass so use are in the of e soil stabilization and solidification However in using pregem g g and pamcular reference heremafier a tos s' successive mJCCUOHS of the different reactants which herei 3; fgg fg is es iany concerned with tofore generally have been necessary to avoid premature pee positions of WW gelling, it has been found that there frequently occurs an factory in many app 1 Ions, e present invcmion also undesired gelation at the immediate site of in ection which comprises compositions which additionally contain a a,

tegqs there to i the soil.pores a preveni uniform active s l of reactii'i with the alkali metal s mixing and reaction of the silicate with the gelling agent. %%m ate y or F g g g gf x z i ii fl g gz iz f 2 substantially water-insoluble gel. When no such reactive secfons 5 ti e g 4 salt is employed, the advantages of this invention are 1 ere S on 8 achieved but in some instances, using a relatively low Perhaps the most common expedient employed m an concentration of amide, the silica gel initialy formed is effort to avoid the disadvantages of the injection of two slow] y soluble in water. Such gels become water-insolreactants has been a dehberate dilution of the silicate uble in a fairly short time even without the addition of and gelling agent, such as calcium chloride, to provide a 5 a reactive salt. However, it will be appreciated that in z ggfi gg g zg g g iggg fi gzzg ig gisg gz some applications, for example, in the treatment of soil mixture into the soil. However, except in those instances fi s a tz g g a 3: 2;: 3:25; g g g s ggw g where it is desired to employ a dilute solution as hereinth 5 f ed after explained, in addition to the disadvantage of han- 'P' we Amrdlngiyi dung large volumes of dilute aqueous ms with the 0 such a situationit is a preferred practice of this mvention that the silicate-amide composition employed addiresultant increased equipment costs a perhaps more ionall contain a reactive salt for the sol urpos o significant disadvantage of such a procedure is that the pmvidi'ng a high degree of initial watepigsglubilit;

strength of the resultant gel is relatively low when rethe initial 51 f0 mme actants in extremely dilute form are employed. amide smca%e nacfive salt g s: componen 1 e Accod'l t'th rin"a1b'tfthis' ti 55 P95 I mg 1 1s e p up mven P Generally, the process of this invention comprises conto f dlflicumcs offhe an tefhmques of tacting soil to be treated with a composition consisting sohliificatlon and to q y? lmpmwd essentially of a single liquid mixture comprising an aque- Posmon adapted for use m Stablhzanon' ous alkali metal silicate, an amide as previously defined A further object of this invention is to provide a new and if desired a reactive salt nerau added in the and Improved alkah metal sfllcate'comammgi 'gelable 0 form of an aqueous solution. 'Ihg amide and silicate can tgnposition of controllable water-insolubility and gel be so proportioned as to provide a reaction or emu ,mrnperatunesw Thesfe and other oblects and advantages the BZWBi: reactive salt need hit W111 appaar more fully from the following descnp' ployed unless a high degree of initial gel water insolubility tion thereof.

Broadly, the present invention comprises the use of a 5 35;52 :221 In any ga g} g g g i g g li 0f matter and using such 'e'e e ii nr s'n neon in eeiioa wner'e'ii'ean position comprising an aqueous alkali metal silicate and be used as a soil impregnam uniformly flmmg in the soil an amlde having the structure 'to an extent dictated by pressure applied, soil porosity and 0 permeability. The undesired premature gelling of prior -5 single treatment solutions, i.e., so-called one-shot treatinstances, the

ments and the low strength of gels formed from prior highly diluted reactants is avoided while there is achieved a rigid gel of high strength and fluid impermeability.

1n the discussion of the invention thus far it will be understood that the composition of this invention incorporates at least suflicient water to render the composisition fluid. However, except in those instances where a dilute solution is desired for reasons of economy or as hereinafter indicated, substantial dilution is to be avoided since it is not necessary as it was in the prior art practice in order to prevent undesired premature gelling and since the presence of a high proportion of water represents an added burden to the equipment. Generally, at least a portion of the necessary water may advantageously be incorporated by using a commercial aqueous alkali metal silicate, typically of alkali metal oxide-SiO, solids content of about 35 to 45%, with additional water being added, if desired, as by admixture of the water with the amide and/or any reactive salt which may be employed.

The term reactive salt as used in the specification and claims is intended to mean those metal salts which chemically react with aqueous alkali metal silicate to produce a completely or substantially water-insoluble silica gel.

It will be appreciated that the proportions of amide, silicate, added water and reactive salt, as well as the amount of soil treated with a given quantity of such a composition varies widely depending upon the porosity, permeability and type of soil, nature of substrata if subsoil applications are intended, and the like. Accordingly, it generally is not feasible to define in terms of proportions a composition which represents an optimum material for use in all types of soil solidification and/or stabilization operations.

However, in many instances it has been found that for practical purposes, using a commercial aqueous alkali silicate, e.g., sodium silicate, typically containing about 35 to 45% solids, excellent results are obtained when there is combined with about 25% to 98% by volume of the total mixture of such an aqueous silicate about 2 to 30% by volume of the total mixture of an amide previously defined herein, especially about 2 to 30% by volume of formamide, the balance being M which may present in an amount of to 6 times the volume of aqueous commercial silicate en a reactive salt is incorporated as a'ii'aqiieous solution, its concentration should be within the range from about 25 g.p.l. to

saturation; the amount of such a solution use s on e within me range from 0 to 100% by volume of the commercial aqueous silicate plus any added water.

It is a feature of this invention that in many instances commercial aqueous silicates can be used in undiluted form with undiluted liquid, or saturated aqueous solutions of normally solid, amides. At times, however, generally at temperatures less than room temperature or when it is desired to treat a large volume of soil to prevent waterflow therethrough, it is desirable to increase the water content of the mixture somewhat as, for example, using one volume of commercial aqueous sodium silicate, containing 35 to 45% solids, with up to 6 volumes of water.

However, water addition is not essential, especially at temperatures greater than room temperature and when a high strength gel is required, it is better to add little, if any, water to the aqueous commercial silicate.

The amount of reactive salt, when used, is insufiicient if used alone with the silicate, to form a satisfactory gel. As indicated hereinbefore, in general, the amount of reactive salt, typically added as an aqueous solution, preferably comprises about to 25% by volume of the total composition. For example, advantageous results are obtained using about 5 to 25% by volume of an aqueous solution containing about 75 g.p.l. of sodium aluminate or 5% by volume of a 50 g.p.l. by weight solution of calcium chloride.

then nux In order that those skilled in the art may more completely understand the present invention and the preferred methods by which the same may be carried into efiect, the following specific examples are offered:

Example 1 Example 2 To 50 ml. of sodium silicate lNa O:3.3SiO 41 B. at 20 C. and 37.98% total solids, is added 20 ml. of distilled water and 10 ml. of fgrmamawith continued stirring. The resultant liquid is clear an exhibits no immediate increase in viscosity. 20 hours after mixing, the liquid silicate-formamide mixture has changed to a hard, tough solid.

Example 3 To illustrate the effect of amide concentration on gel time, tormamide and water are premixed in varying proportions and a ded to undiluted aqueous sodium silicate 1Na,O:3.3Si0, (41 B6. to 20 C.-total solids of 37.98% by weight), the solution temperature being maintained at 25' C. The results are as follows:

Silicate, Form- Water, Time to Gel Ml. amide, Ml. (hours) 50 10 20 2 and 10 min. 60 12 18 1 60 14 16 2 mlnutes Example 4 Into a split plastic mold is placed 250 g. of -60 mesh dry Ottawa silica sand. 50 ml. of a mixture comprising ml. of undiluted sodium silicate solution of the preceding example, 25 ml. oflgaegideand 35 ml. of water is prepared and poured into t e sand mold. Gelation occurs in 45 minutes.

Example 5 Silicate-amide gels are prepared by adding water to formamide to form 30 ml. of solution which is into 50 ml. of aqueous sodium silicate (lNa,0:3.3SiO,, 41 B. 22 C.) and the gel time observed. The results of such tests when the gel temperature is held at 26 C. are as follows:

Silicate, Form- Water, Gel Time,

Ml. amide, Ml. Minutes Example 6 There is prepared a composition of this invention consisting of 100 ml. of aqueous sodium silicate (1Na,0:3.225i0,, 41.5 B. 20 C.) (62.5% by volume), 40 m1. of water (25.0% by volume) and 20 ml. of formamide (12.5% by volume). The increase in viscosity observed while maintaining the mixture temperature at 28 C. using a Brookfield Viscosimeter with continuous agitation is as follows, the viscosity being expressed in terms of centipoise:

To illustrate the effect of varying proportions of amide, a series of tests is carried out with the aqueous sodium silicate of the preceding example, formamide and water are prepared. The results of such tests are indexed comparatively as follows:

Silicate, Form- Water. Gel Time,

Ml. amid Ml. Minutes Example 8 To illustrate the advantageous insolubilizing effect in certain instances of incorporating a reactive salt with the silicate-amide composition, there is prepared a mixture of 50 ml. of aqueous sodium silicate (1Na O:3.3SiO 40.0-41.2 B.37.3% solids), 5 ml. of formamide and 24 ml. of water. This mixture, which els in six hours, is split into two portions; one being placed in disiilEd water where it softens and dissolves, the other sample, placed in an aqueous solution containing 500 p.p.m. of calcium chloride and sodium chloride combined hardens and remains insoluble. This solution is typical of ground water frequently occurring in practical application of soil stabilimtion materials.

Example 9 Two sand cylinders are prepared by mixing 250 g. of 60 mesh silica sand with 50 ml. of a solution prepared by mixing 100 ml. undiluted aqueous sodium silicate (1Na,O:3.3SiO specific gravity 1381-1397), 25 ml. formamide and 35 m1. of water and pouring the 50 ml. of this solution into the sand while it is retained in a mold. The thus-formed sand cylinders are air dried for three days, one cylinder being retained as a standard sample and the other being placed in a beaker of water and allowed to stand in contact with water for a month and a half. No solubility is noted in the immersed cylinder after seven weeks immersion, thus indicating that the gel produced by combining only an alkali metal silicate and an amide achieves a high degree of insolubility.

Example 10 A cylinder of sand (60 mesh Ottawa silica sand) is prepared using a mixture of 8 ml. (6% by volume) formamide, 60 ml. of sodium aluminate g.p.l., 15% by volume), 92 ml. of water (19% by volume), 120 ml. of aqueous sodium silicate (lNa O:3.22SiO 40.0-41.5 B.), 120 ml. of water being added to the silicate, and maintaining the mixture temperature at 29 C. The mixture is then poured into a mold and the sand added. To fill the mold (9.132 cu. in.) there are employed 254 g. of sand and 50 ml. of the gellable mixture.

Example 11 Test cylinders (1 dia. x 3" high) of sand are prepared using -60 mesh Ottawa silica sand, the compositrons and strengths being as follows:

Composition of Gelable Liquid, Percent by volume Oompres Sand Liq. sive Sodium (8-) strength Formamide Alumi- Water, Sodium ,51

nate. 75 Ml. Silicate l g.p.l.

l 1Naq0:3.22SlO,, av. 37.5% solids-diluted with equal volume. 1 Same silicate but undiluted.

Example 12 The following are illustrative of other compositions of this invention:

Sod. Alumi- Viscosity 1 Formnmide nate (ml. H O Sili- (ml.) of 75 g.p.l. (ml) cate l soln.) (m1.) initial 1 hr.

1 In oentipoise measured by Brookfield visoosimeter. At M hour. 4 At 42 minutes.

Example 13 Using an aqueous sodium silicate (1Na 0:3.22SiO 40.0-41.5 B., av. solids 37.5%) diluted with an equal volume of water, there are prepared the following compositions having the indicated pumping life and gel times:

8 Example 14 What is claimed is: Other illustrative compositions of this invention, 1. The method of treating soil which comprises conwherein the numerical values are in terms of percent by tacting said soil with a single liquid composition of volume, are the following: matter consisting esesntially of an aqueous alkali metal GomposlttonNo -123456 Sodium 1 60606060606000 so (so (100 (50 m Composition Nosilicate (100 (50 g.p.l.)

Composition No Bodlum silicate 1 80 (50 (100 g.p.l.) (50 3. 2.1.)

l 1NazO:3.3Si0| and alternatively, 1Na O:3.22SlO 1 A: aqueous soiutlon containing 75 g.p.l. sodium te. Norm-Other illustrative compositions of this invention are those as set forth above wherein the amide and/or reactive salt concentration is or by volume, the silicate being reduced accordingly.

Example 15 silicate having an alkali metal oxidezsilicon dioxide ratio of about 13.0 to 124.0 and containing about to g gg ffiz 3 22 53 3: g s; 3:2 :22, solids, water and about 2% to 30% by volume of an by volume, are the following: 55 amlde of structure ll Composition No 1 2 3 B C NH wherein R is selected from the group consisting of H,

Sodium sill to 415 B. 20 0. 62.5 e0 Added g 9 u 25 21 1&5 6 lower alkyl, --CONH, and lower alkyl substxtuted amldo Fornlamlde 12 5 14 14.0 groups.

in water) 5 2. The method according to claim 1 wherein the amide is formamide.

The term soil as used in the specification and claims 3. The method according to claim 1 wherein the comis intended 6 refer to various types and compositions of position also includes about 5% to 25% by volume of soil, including sand, loam, porous or fissured rock, and the total composition of an aqueous solution containing the like, for example, as described in pages 614 to 633 50 to grams per liter of a metal salt capable of of volume 12 of the Kirk-Othmer Encyclopedia of Chemreacting with the alkali metal silicate to produce a waterical Technology and on page 785 of Hackhs Chemical insoluble silica gel, said metal salt being a salt of a metal Dictionary, third edition. selected from the group consisting of alkali metals,

It is to be understood that although the invention has 79 alkaline earth metals, aluminum, iron, copper and zinc. been described with specific reference to particular cm- 4. The method according to claim 1 wherein the combodiments thereof, it is not to be so limited, since changes position also includes about 5% to 25% by volume of and alterations therein may be made which are within the total composition of an aqueous solution containing the full intended scope of this invention as defined by the about 50 to 100 grams per liter of a reactive salt selected appended claims. 7 from the group consisting of sodium aluminate, sodium bicarbonate, ferric chloride, aluminum chloride, cupric sulfate, cupric chloride, zinc chloride and calcium chloride.

5. A soil stabilizing composition of matter in the form of a single liquid composition of matter consisting essentially of to 98% by volume of an aqueous sodium silicate having an Na=OzSiO ratio of about 1:3.0 to 1:4.0 and containing about to solids, about 2% to 30% by volume of formamide, and 5% to 25% by volume of an aqueous solution containing to grams per liter of sodium aluminate and the balance water.

6. Soil stabilized by admixture with a composition consisting essentially of an aqueous alkali metal silicate 10 having an alkali metal oxidezsilicon dioxide ratio of about 13.0 to 1:4.0 and containing about 35% to 45% solids and about 2% to 30% by volume of formamide.

References Cited in the file of this patent UNITED STATES PATENTS 1,827,238 Ioostcn Oct. 31, 1931 2,069,486 Tilden Feb. 2, 1937 2,437,387 Hodgson Mar. 9, 1948 2,575,170 Holmes Nov. 13, 1951 2,717,884 Mon-ill Sept. 13, 1955 2,766,130 Dietz Oct. 9, 1956 2,809,118 Keil Oct. 8, 1957 2,899,330 Lyons Aug. 11, 1959 

1. THE METHOD OF TREATING SOIL WHICH COMPRISES CONTACTING SAID SOIL WITH A SINGLE LIQUID COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF AN AQUEOUS ALKALI METAL SILICATE HAVING AN ALKALI METAL OXIDEISILICON DIOXIDE RATIO OF ABOUT 1:3.0 TO 1:4.0 AND CONTAINING ABOUT 35% TO 45% SOLIDS, WATER AND ABOUT 2% TO 30% BY VOLUME OF AN AMIDE OF THE STRUCTURE 